On-line help

There are are five sources of information for a Linux system: (1) manual pages, (2) info pages, (3) HOWTOs and documentation for programs, (4) help from programs and (5) the Internet Google search engine.

• Man pages: On-line manual pages available on every Linux system. These are often the best sources of reference information about various programs on the system. Here are some useful pointers about man pages.
  • You want to know more about a certain command or program. To find out about a command and a description of what it does, type man <command_name>. Sometimes there may be more than one command with the same name. For example sleep <secs> command sleeps for the specified number of seconds. There is another man page for the sleep system call that you can call from a C/C++ program. Typing in man -a sleep will show you all the man pages for sleep. It will show the first man page. If that is not the one you want, then press q to quit that page and then it will show you the next one on the same command and so on. You can use
    em Page Up and Page Down keys to browse a manual page.

  • You want a one line summary of what a command does. To obtain a one line summary about a command type man -f <command_name>.

  • You want to find a command that does something you want to do. Use a appropriate keyword that best describes what you are looking for and then type man -k <keyword>, which displays one line summaries of the commands that reference that keyword. For example:

    [amit@onyx]: man -k sleep
    Tcl_Sleep            (3)  - delay execution for a given number of milliseconds
    Tcl_Sleep [Sleep]    (3)  - delay execution for a given number of milliseconds
    apmsleep             (1)  - go into suspend or standby mode and wake-up later
    nanosleep            (2)  - pause execution for a specified time
    sleep                (1)  - delay for a specified amount of time
    sleep                (3)  - Sleep for the specified number of seconds
    usleep               (1)  - sleep some number of microseconds
    usleep               (3)  - suspend execution for microsecond intervals
    

    The numbers in the second column show the Section umber for the manual page. So now we see several commands/calls that are related to sleeping. Find out more by doing man 3 sleep or man 1 sleep, where the number is the section number.

  • Man pages are organized into sections. The following shows the different sections and what they logically contain.

    Section	The human readable name
    1	User commands that may be started by everyone.
    2	System calls, that is, functions provided by the kernel.
    3	Subroutines, that is, library functions.
    4	Devices, that is, special files in the /dev directory.
    5	File format descriptions, e.g. /etc/passwd.
    6	Games, self-explanatory.
    7	Miscellaneous, e.g. macro packages, conventions.
    8	System administration tools that only root user can execute.

    For example, if you want to find out more about the printf library call, you can simply look for it in Section 3 using the following command:

    man 3 printf

    Otherwise if you say man printf, you will get the first man page found, which happens to be in Section 1. This command describes a printf that you can use from the shell and is different from a printf used in a C program.

• Info: Info will generally provide a gentler introduction than the man pages. However, it is more complicated to use; info gives a topics menu on starting up. A first-time user can type h for a tutorial on how to use info. Suppose you want information on the topic <topic>, then use info <topic>. For example, try info passwd.

• HOWTOs and program documentation. Linux has hundreds of excellent HOWTO documents available that describe specific topics. Go to to the website http://www.linux.org and look under the documentation section for a list of available HOWTOs. On your local system, look in the directory /usr/share/doc. There are hundreds of subdirectories, one each for specific programs that have more detailed information about that program.

• Ask a program: Many programs will display a message describing how to use the program when supplied with the command line option --help. For example, try

  passwd --help

• Google it! One of the best and fastest sources of information is the Google search engine on the Internet. Point your browser to www.google.com. Get familiar with this search engine and you may save years in your life.

• KDE Help. Under the KDE GUI desktop, you can access all the man and info pages in an integrated fashion. Type Alt and F2 together. It will pop up a window. In that window type in man:cmd or info:cmd to access the man page or info page for the command cmd. Try this: Alt and F2 to get a popup window, then type man:submit.